The traditional Fourdrinier papermaking process essentially consists of three steps, performed in succession in corresponding sections of the papermaking machine: the forming section, the press section, the dryer section.
In the forming section, an aqueous pulp of cellulose fibre (possibly also containing other components) is applied to a forming fabric in the form of an endless belt supported by rollers. The removal of water from the pulp through the forming fabric gradually leads to the formation of a strip of damp paper material, which still has a relatively high water content. More water is removed in the press section, where the paper material is pressed as it passes between one or more pairs of rollers. The paper material is then sent to the dryer section where it undergoes a final water-removal process. The paper thus formed is ready to undergo subsequent finishing and packaging processes.
As is common practice in the papermaking and papermaking fabric industry, in the following description the terms “machine direction” (abbreviated to “MD”) and “cross machine direction” (abbreviated to “CMD”) are used to indicate respectively a direction corresponding to the direction of the flow of the forming fabric in the papermaking machine, and a direction parallel to the surface of the fabric and crosswise (orthogonal) to the direction of the flow. The direction or orientation of the weft and warp yarns of the forming fabric are also indicated with reference to the machine direction and cross machine direction.
Again as is common practice in the sector, the surface of the forming fabric that comes into contact with the cellulose pulp (i.e. with the paper material being formed) is the top surface of the fabric; and the opposite surface facing the machine is the bottom surface. This reference is also used to describe the vertical spacing of the yarns in the forming fabric.
Although different types of fabrics suitable for use in the forming section are known in the prior art (such as those described, for instance, in U.S. Pat. No. 4,515,853, U.S. Pat. No. 3,885,603 and U.S. Pat. No. 6,145,550), there still appears to be room for improvement in this sector, for example in terms of mechanical strength, stability, life, draining capacity and quality of the formed paper.